Thinking out loud it helps to clear the cobwebs.
I have for a long time wanted to purchase a 4 jaw chuck for the Clausing. But with the L00 mount used chucks were not plentiful around here or on the net. CDCO has one model, plain back, no mount, but they sell the mount also. It's main drawback is no rpm rating. So the search has drug on for a very longtime.
The other day I was searching for dividing head and stumbled on a 4 jaw chuck, 6",8",or 10" independent, with a semi-finished L00 mount . It has an rpm rating of 2100rpm. More than enough for me. Fitting the chuck to the mount is not that complicated, there have been several done here and there a more than a few series on Youtube showing the process. Most all my questions have been answered on that front.
The main question is what size to get?
I have a 8" 3 jaw on the lathe as the only workholding device right now.
Buying a 10" 4 jaw independent chuck id not too much more than the 8" 4 jaw independent is, but would the 10" be too big for my Clausing 6903 14" X 30" lathe?
The title of this thread says, independent vs. scroll....
I am going to buy one of each, the scroll has its uses, one of which is to drill into the end of square stock when dead nuts accuracy is not needed. I might have a production job of that nature, this coming spring. A 5C collet chuck will not work as the pieces are beyond the size range of the collets.
And the 4 jaw independent chuck will get a lot of use once I get started on the crawler again.
I am going to replace the 3 jaw also, but I would like to find a Set Tru or similar chuck to replace it with.
Any comments, ideas, or hard experience will help.
Dan.

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I see no problem at all with the ten inch four jaw, I have a eight inch four jaw on my eleven inch lathe. As long as you can lift it I would go with the ten inch.IMO Nothing wrong with a extra inch or two

The hidden issue with chuck sizing is interference as you open the jaws. it is machine dependent.
I have that issue with one of my lathes where a 10 inch chuck will open wider than a 12 inch. a larger chuck is not automatically a better fit to a lathe.
Some things to consider are weight, opening clearance, how far out from the spindle bearing you are and clearance over the cross slide.

Chris, maybe if the 3 jaw was tighter,(less wear in it) I could try that. It is pretty loose, there is a plan for it eventually.
Digr, thanks for the information. I am just leery of buying the 10" and find out it is too large for my lathe.
If the weather does not get too bad in January, I should be able to get at the frames that were dumped there 10 years ago. They were from a grain dryer shelter, roof with no walls. Their new dryer did not fit under the roof and the roof would not cover it. When the contractor took the old structure down they just hauled the frames ad roof purlins over to the wood line and dumped them. The old man decided not to sell them or let someone have them, they just laid there in a ppilesince then. The son, who I have done work for called me a couple of months ago to see if I wanted them. I went over and looked at them. Buried under 10 years of brush and blackberry brambles. On top of that when the old man put the new truck driveway in, he backed up a lot of water into that area. Turning it into a mudhole more than ankle deep, over the top of Lacrosse 18" burly's. Need about a week of freezing weather to be able to get into the area with his Deere 333 mini trackloader to haul the parts out of the brambles.
Each of the bents had a chainfall that ran on the parallel beam header, if I can recover all of them, I can build a rolling bridge crane with them. Fred, (the son) has been wanting to clean up that area up for two years now. The old man is in a nursing home, and does not know anyone anymore. So he will never miss them. Too bad, other than being a four star jerk at times he was a nice guy. Paid well and quickly.
I tried to deal on them several times, but could never come to a bargain on them.
Dan.

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A 3-jaw chuck is a 3-jaw chuck, it will have "X" amount of runout, a set tru is a waste. If you keep the work in the 3-jaw chuck for all operations, then the part will be dead nuts true and concentric.

If you need to move the work between operations than you either need to turn it between centers or put it in an independent 4-jaw chuck and dial it in after each move. A 4-jaw scroll jaw chuck is useless as far as I'm concerned. If you have a production job to turn square or other than round material than a 5-C pot chuck or custom soft jaws in an 3-jaw scroll chuck would be my choice.

As far a chuck size goes, I look at it just like sizing a lathe or another machine. You can put small work in a big chuck but you can't put big work in a small chuck.

__________________
Mac
___________________________________________
One extremely happy former convict of the penal colony that lies between NY, PA, and DE. Now living the good life much further south. where they don't know what fucking Carhartts are.

The hidden issue with chuck sizing is interference as you open the jaws. it is machine dependent.
I have that issue with one of my lathes where a 10 inch chuck will open wider than a 12 inch. a larger chuck is not automatically a better fit to a lathe.
Some things to consider are weight, opening clearance, how far out from the spindle bearing you are and clearance over the cross slide.

Terry, I have thought of making circes to match the size of the various chucks I am looking at. I would use them to check clearances.
As to stick out from the front bearing, if I read the drawings correctly, the 4 jaw's weight is closer to the bearing than my current 3 jaws weight is.
Thanks.
Dan.

__________________
Tools to Men are like Shoes to Women , you can never have too many !!
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...A 3-jaw chuck is a 3-jaw chuck, it will have "X" amount of runout, a set tru is a waste. If you keep the work in the 3-jaw chuck for all operations, then the part will be dead nuts true and concentric...

I tend to agree about set-tru chucks. They're only good at the one point where you set them, otherwise you still have a 3-jaw chuck with it's inherent runout.

Having said that, as far as I'm concerned--for the work that we do--a 3-jaw is more than adequate for most things. I am constantly making parts in a 3-jaw and swapping them end for end to finish off--the few thou of runout that you pick up often doesn't matter.

If your lathe is capable of parting off efficiently an awful lots of parts can be made in a 3-jaw with most of the features concentric to each other. Often all you need to do after parting off is to face the "back" side which, in many different situations, doesn't need to be perfect in relationship the the rest of the part.

Quote:

...A 4-jaw scroll jaw chuck is useless as far as I'm concerned...

There aren't a lot of uses for 4-jaw scroll chucks but, like every other tool in the box, they do have their place. If you're machining round features on square stock they can be really handy--dialing square stock in on a 4-jaw is a pain in the ass.

As far as the size of your 4-jaw I think a 10" is just about the right size for a 14" lathe...

__________________Keith

Measure twice and cut once...or...wait, was that the other way around?

Mac, the problem with 5C collet chuck for the production job, is the stock size, 2"+ square. I am not sure of the real size as I have not seen the prints yet. The last shop that did the job, messed it up to the point of about 1/3 of the run was scrap. The major tolerance bugaboo is length, + .002 / - .000. Hole is drilled than a form tool is run in to a certian depth. It is a goofy part, not too hard to make but finicky.
Another one of the no photos allowed jobs, I get once in awhile.
I could set up the job in the independent 4 jaw. It would be a little more work but it could be done.
Dan.

__________________
Tools to Men are like Shoes to Women , you can never have too many !!
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Keith, yes I have made many parts in a 3 jaw chuck, just the way you suggest. Most of the time it works out fine. Until you run into a repair, either a weld up &turn back to size or a turn and sleeve. Those I want the 4 jaw indie for.
The 4 jaw scroll would be paid for and then some after the first 150 parts. These are not Buck, Bison or another high quality/expensive chucks. But for now they would fill the gap for me. My biggest problem is finding backing plates in the L00 taper mount. I most likely would be able to turn my own once I get the shop better tooled up. But for now, beggars can't be choosers when it comes to that taper.
I went anf looked at another lathe, if the owner comes down on it somemore then I would have a Lodge & Shipley 22" swing, with a boat load of tooling, 8 or 9 chucks, taper attachment and DRO. I can't remember the model off the top of my head just now but it is tight clean and little used. Owner thinks it is of late 60's early 70's manufacture. Big heavy beast, estimate it weighes in at around 10 - 12,000 pounds. Chucks a D- style. Can stay where it is at until the weekend before 4th of July 2019. He inherited it from his grandfather with the house and land. He has sold the rest of the machine tools that were there. He is in no hurry to get it moved as we will ha e to remove the one wall to get it out of the shop. The c - c is around 96" , that is why no one wants it.
Dan.

__________________
Tools to Men are like Shoes to Women , you can never have too many !!
Used diesel engines are an adventure anyway you look at them !!
Miller XMT-304 Multiprocess
Miller 10-E Wire Feeder
Miller Spectrum 2050 Plasma Cutter
Hobart AC/DC stick welder
Hobart 175 Mig
Craftsman O/A set
Turbo torch and B-tank